1. Field of the Invention
The present invention relates generally to an optical receiver module, and in particular, to an optical receiver module with a top open can (hereinafter referred to as “TO-Can”) structure for high-speed optical communication. The optical receiver module may include a photo diode for converting an optical input signal into an electric current.
2. Description of the Related Art
In order to meet the increasing demand for optical communication capacity, high-speed optical communication systems capable of supporting a rate of 10 GHz or higher have been developed. Such systems may include optical receiver modules having a butterfly structure in which active devices for optical transmission/reception are integrated on a flat form-type substrate, and a TO-Can structure in which the upper side of a stem on which active devices for optical transmission/reception are integrated is covered. Such optical modules have a low manufacturing cost and can widely be applied to various types of high-speed optical communication systems.
FIG. 1 is a perspective view illustrating a conventional optical receiver module 100 with a TO-Can structure. Referring to FIG. 1, the conventional optical receiver module 100 includes a stem 101 with a plurality of holes formed thereon, a plurality of leads 102, a photo diode (PD) or POB(PD on block) 130, and a trans-impedance amplifier (TIA) 110.
The photo diode 130 is mounted on an upper side of the stem 101, and converts an optical input signal into an electric current. The photo diode 130 has two terminals 131: one is an anode and the other is a cathode. The trans-impedance amplifier 110 amplifies and converts the electric current received from the photo diode 130 into high frequency (RF) signals having opposite phases, and conducts (or transmits) the amplified RF signals to the respective leads 102. To output the RF signals, the trans-impedance amplifier 110 includes two output terminals 111 for outputting the RF signals having the opposite phases.
The holes 103 (shown in FIG. 2), through which the leads 102 pass, are filled with sealing glass (not shown). The leads 102 may be fixed to the stem 101 at the same time the holes 103 are sealed. The leads 102 are connected to the trans-impedance amplifier 110, and classified into signal leads for outputting the RF signals to the outside of the optical receiver module and direct current (DC) leads for providing electric power to the photo diode 130 and the trans-impedance amplifier 110. The signal leads and the DC leads have the same shape.
The trans-impedance amplifier 110 is connected to the photo diode or POB(PD on block) 130 with a conductive wire 105 by wire bonding. Also, the leads 102 protruding from the upper side of the stem 101 are connected to the trans-impedance amplifier 110 with conductive wires 105 by wire bonding.
However, in the conventional optical receiver module, the trans-impedance amplifier 110 is directly connected to the conductive wires 105, causing an extensive increase in length of the conductive wires. The increase in length of the conductive wires 105 increases impedance and inductance. The increase in impedance of the conductive wires 105 causes impedance mismatching between the trans-impedance amplifier 110 and the leads. The leads 102 protruding from the upper side of the stem 101 add the inductance. Generally, the leads surrounded by glass seal 103 are not matched to 50 ohm.
Due to the impedance mismatching between the trans-impedance amplifier and the leads, parts of the RF signals output from the trans-impedance amplifier 110 are reflected from the leads back to the trans-impedance amplifier 110. Since a portion of the RF signals is reflected, the signal strength and bandwidth of RF signals output to the outside of the optical receiver module are reduced.
In addition, the impedance mismatching between the trans-impedance amplifier and the signals leads is increased when the optical receiver module is used for high-speed optical communication network. There is, thus, a need in the art for an optical receiver module with the TO-Can structure that can be used with high-speed optical communication network.